1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which has the electrophotographic photosensitive member. More particularly, it relates to an electrophotographic photosensitive member having a surface layer containing a specific resin, and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
2. Related Background Art
Conventionally, inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide have widely been used in photosensitive layers of electrophotographic photosensitive members. In recent years, research has been actively conducted on the use of organic photoconductive materials in the photosensitive layers of electrophotographic photosensitive members because they are very safe, are suited for mass production and are low in cost. A large number of photosensitive members have been proposed and put into practical use.
Mechanical external forces ascribable to charging means, developing means, transfer means, cleaning means and so forth are directly applied to the surfaces of electrophotographic photosensitive members, and the photosensitive members are required to have durabilities to these.
Since usually the organic photoconductive materials do not have any film-forming properties for themselves, they are commonly formed into films by the aid of binder resins. Accordingly, the mechanical durabilities of electrophotographic photosensitive members making use of organic photoconductive materials greatly relies on the selection of binder resins. Polystyrene, polymethyl methacrylate, and polycarbonate resin of bisphenol-A or bisphenol-Z type are conventionally used as the binder resins. In particular, the polycarbonate resin of the bisphenol-Z type is widely used as a binder for photosensitive members of medium- or low-speed copying machines or laser beam printers, and has greatly contributed to contemporary advancement of the electrophotographic photosensitive members making use of organic photoconductive materials.
However, further durabilities have had to be imparted to the photosensitive members in order to achieve their expansion to high-speed copying machines and to reduce copying cost.
Stated specifically, the photosensitive members are required to have further durabilities to wear and scratching of photosensitive member surfaces caused by friction and to deterioration of photosensitive member surfaces caused by ozone which tends to be generated at the time of corona charging in an environment of high humidity. Also, there is such a problem that toners may adhere to photosensitive member surfaces because of the repetition of development and cleaning. It is sought to improve cleanability of photosensitive member surfaces to cope with such problems.
In order to satisfy such various properties required for the photosensitive member surfaces, it has been variously attempted in variety to provide on the photosensitive layer a surface protective layer composed chiefly of a resin. For example, Japanese Patent Application Laid-open No. 57-30843 discloses a protective layer whose resistance has been controlled by adding metal oxide particles as conductive particles.
Studies have been conducted on adding substances of various types in surface layers so as to improve physical properties of photosensitive member surfaces. For example, because of the low surface energy of silicones, additives such as silicone oils (Japanese Patent Application Laid-open No. 61-132954), polydimethylsiloxanes, silicone resin powders, cross-linked silicone resins, poly(carbonate silicone) block copolymers, silicone-modified polyurethanes and silicone-modified polyesters have been reported. Also, typical polymers having a low surface energy include fluorine type macromolecules. The fluorine type macromolecules may include polytetrafluoroethylene powder and carbon fluoride powder.
The surface protective layers containing metal oxides can provide layers having a high hardness. However, such layers tend to have a large surface energy and hence tend to cause a problem on their cleanability. The silicone type resins are advantageous in view of a small surface energy, but have insufficient compatibility with other resins. Hence, they have had specific problems in that, when added, they tend to agglomerate to cause light scattering or to bleed and thus localize at the layer surface, thereby exhibiting unstable performances.
The fluorine type macromolecules are also commonly insoluble in solvents and also have a poor dispersibility. Hence, they have had problems such that smooth photosensitive member surfaces can be formed with difficulty, and light scattering tends to occur because of a small refractive index to cause a deterioration in transparency. The fluorine type macromolecules also have such problems in that they are commonly so soft as to be readily scratched.
In addition, the use of surface protective layers or additives is attended by a bad effect that they may worsen electrophotographic characteristics such as sensitivity and residual potential.